1. Field of the Invention
This invention relates to AC powered ionizers for that are used for static charge control. More specifically, the invention is targeted at the problem of ion emitter contamination in the AC ionizers, while the ionizer performs useful neutralization.
With AC ionizers, each emitter receives a positive voltage during one time period and a negative voltage during another time period. Hence, each emitter generates both positive and negative ions.
Both positive and negative ions are directed toward a charged target for the purpose of neutralizing the charge.
2. Description of Related Art
Ion emitters generate both positive and negative ions into the surrounding air or gas media. To generate ions, the amplitude of applied AC voltage must be high enough to produce a corona discharge between at least two electrodes, where at least one of them is an ion emitter.
The minimum voltage for the establishment of corona discharge is called corona onset voltage or the corona threshold voltage. According to theoretical and experimental studies of corona discharge this voltage mainly depends upon the ion emitter geometry, polarity of applied voltage, gas composition and pressure [F. W. Peek, “Dielectric Phenomena in High Voltage Engineering” McGraw Hill, New York, 1929 and J. M. Meek and J. D. Craggs “Electrical Breakdown of Gases” John Wiley & Sons, Chichester, 1978].
For wire or filament-type ion emitters, the corona onset voltage is typically in the range of positive 5 to 6 kV for positive ionizing voltage and in the range of negative 4.5 to 5.5 kV for negative ionizing voltage. For point-type ion emitters, the absolute values of onset voltage are typically 1-1.5 kV lower. These stated corona onset voltages apply to clean emitters. If the emitters are not clean, corona onset voltages change.
It is known in art that airborne particles from the surrounding air or gas accumulate on the emitters. Effectively, the emitters are functioning as electrostatic precipitators. Emitter contamination is an expected consequence of corona discharge in open air. Contamination buildup changes the emitter's geometry and raises onset voltage.
Once contaminated, real time ion production decreases, and the efficiency of the AC ionizer decreases significantly. This buildup must be removed to restore proper operation of the ionizer. In large facilities, thousands of emitters are present. Contamination removal becomes a large and objectionable use of resources.
Prior art contamination removal methods include manual brush abrasion and automatic brush abrasion. These methods of mechanical cleaning are effective, but require additional mechanical parts or operator time. In some cases, abrasive cleaning transfers contamination accumulated by ion emitters to the product, which must be kept clean.
A new method is needed to reduce the contamination deposition rate on the ion emitters. Ideally, the method would arise from basic physics or electronics, and operate without taking the ionizer out of service.
Further, the contamination prevention method should apply to a variety of emitter configurations: points, wires, filaments, or loops.